This invention relates to voltage regulators. In particular, this invention relates to switch-mode regulators.
Switch-mode regulators, or switching regulators as they are commonly known, are typically used as voltage regulators because they exhibit higher efficiency than an equivalent linear regulator circuit at heavy loads. A typical switching regulator operates by repeatedly turning a power switch fully on and then fully off, generating a pulse-width modulated signal that is averaged to the final voltage with an inductor. Due to the switching nature of the power transistor drive, the efficiency of a typical switch-mode circuit falls off as the load decreases, since a fixed amount of power is wasted in the drive circuitry regardless of load. One method used to avoid this efficiency loss at light loads is to sense the current flowing in the output, and to omit switching cycles when the load is light. This is referred to in this description as Burst Mode.TM.. Stated another way, burst mode is a mode of operation which uses the technique of cycle-skipping to reduce switching losses in a switching regulator and increase the operating efficiency at low output current levels.
Burst mode is relatively easy to implement in a current-feedback regulator, since the output current signal is available to the regulator to allow it to decide when the load is light. A typical voltage feedback switching regulator does not have this load current signal available, and must make the decision to enter burst mode in another manner.
In view of the foregoing, it would be desirable to provide a circuit and a method for enabling a voltage-mode feedback switching regulator to enter and exit burst mode automatically.
It would further be desirable to provide a technique for enabling a voltage-mode feedback switching regulator to enter and exit burst mode automatically for both synchronous and non-synchronous topologies of the voltage-mode feedback switching regulator circuit.